1. Field of the Invention
This invention relates to an improvement in a splicing member for splicing optical fiber cables and in one aspect relates to a new splice element having a torsional strain relief member to engage the buffer or jacket of the optical fiber cables being spliced to restrict buffer rotation, maintain the buffer in the splicing member and to relieve torsional stress from being transferred to the core fiber and cladding, restricting fiber breakage induced by torsion, particularly in 900 um buffered fiber. A further aspect of the invention is an improvement in the splicing tool used to complete the splice.
2. Description of the Prior Art
The commercially available splice element as disclosed in U.S. Pat. Nos. 4,865,412; 4,824,197; 5,102,212 and 5,189,717, and available from the assignee of this invention, provides an effective member for splicing optical fiber cable in the field. When technicians make the splices however and then coil the slack lengths of fiber in a splicing tray, instances of fiber breakage have been reported. This breakage appeared to be occurring almost entirely when relatively long lengths of 900 um fiber were tightly coiled and stored in splicing trays after the splicing members were installed. The fiber broke on the bare glass section between where the fiber entered the clamping or splicing element and the end of the plastic buffer or jacket on the cable. After study of this breakage, it was discovered that this breakage was the result of torsional stress being generated in the slack cable by coiling the stiff buffer coated fiber in the splice tray. During the coiling process, the free end of the fiber being coiled rotates a fixed amount for each coil being made in the fiber. For example, if the fiber is coiled four (4) times in a tray to store the slack, then the free end of the fiber would attempt to rotate four revolutions to relieve the built up torsional stress. Since the fiber plastic buffer coating is torsionally rigid, and because the 900 um fiber usually cannot rotate within its cable, as occurs with loose buffered 250 um fiber, all the coiling induced torsional stress is focussed on the bare glass portion of the fiber where it enters the splice element of the splicing member. If most of the fiber is coiled in storage before the fiber ends are spliced the torsional stress is reduced. The use of a tool for the splicing operation however requires that a certain length of the fibers remain uncoiled. Therefore, a certain amount of stress will be present when splicing 900 um cables. Additionally, it has been noted that the plastic buffer coating on 900 um fiber shrinks back from where it has been stripped when the fiber is exposed to elevated temperatures. This characteristic varies with the type of buffer coating material and the manufacturer.
Strain relief members have been used in conjunction with the sleeves of optical fiber connectors. This is illustrated in such patents as U.S. Pat. Nos. 5,121,455 and 5,452,386. The U-shaped retention members 34 and 35, which are illustrated in U.S. Pat. No. 5,121,455, are narrow plate-like members having U-slots formed in the plates and are inserted through apertures in opposed relation to each other. The U-shaped slots have sharp, inner edges 38 on their legs to penetrate the outermost material portions of the optical fiber cable to retain the cable in firmly, longitudinally retained position within a rigid sleeve of the connector. This is an example of an axial strain relief member in a connector. In connectors, the sleeve is allowed to rotate. It can rotate in the connector or prior to being inserted into the connector. Thus, there is not a build up of torsional stress on the fiber end. A retention member in the connector plug would not negate torsional stress. Further, in U.S. Pat. No. 5,452,386, the fiber fixing clip 12 is stamped from a single piece of sheet metal stock and comprises a flat base 62 from opposite edges of which depend respective fiber retention plates 64, each of which comprise a pair of legs 66 each having a tapered free end portion 68, the legs defining between them an opening 67 having parallel side edges 65, which edges bite into the jacket J of a fiber inserted into the sleeve 8 of the connector. The narrow edges of the legs restrict the axial pull-out of the fiber from the sleeve, but there is no teaching of the clip restricting torsional stress on the stripped end of the fiber that is inserted into connector 102 and the sleeve 8, against the gel 206, and abutting the length of fiber fixed in the connector. Any relief of torsional stress is not needed nor does it appear to be contemplated by the patentee.
U.S. Pat. No. 5,048,920 also illustrates and clearly teaches the use of a clamp 78 to grasp a fiber end and fix the end within a fiber passage. The clamp 78 is not described as used to restrict torsional stress on the fiber end held in compression against the second fiber end. This again is a clear teaching of the use of a plate member having a U-shaped slot which engages the optical fiber end between the narrow opposed edges defining the U-shaped slot.
Additional prior art showing a splicing member is U.S. Pat. No. 4,730,892. This patent discloses a splicing device having a cover and a base housing members 10 and 12, first and second fibers 13 entering the housing member, a pair of clamps 14, 16 for clamping jacketed fiber within the device and a central screw-mounted bias member 18 for clamping stripped fiber ends at a junction zone. The clamps 14, 16 are formed with an elastomer block at the lower end to provide the desired gripping of a jacketed portion of each fiber. This patent is silent about clamping the jacketed fiber to avoid torsional stress on the portion of the glass between the clamp aligning the fiber ends and the elastomer block on the clamp.